Method of manufacturing a silicon carbide semiconductor device

ABSTRACT

A silicon carbide semiconductor device includes: n type regions formed on a surface of the n− type epitaxial layer; p type body regions formed at positions deeper than the n type regions; p− type channel regions each reaching the p type body region; and n++ type source regions formed toward the p type body region from the front surface side of the epitaxial layer, and the p− type channel regions and the n++ type source regions are formed at a planar position where the n type region remains between the p− type channel region and the n++ type source region, and out of boundary surfaces which are formed between the p− type channel region and the n type regions, the boundary surface on an outer peripheral side is positioned inside an outer peripheral surface  116   a  of the p type body region as viewed in a plan view.

RELATED APPLICATIONS

The present application is a divisional application of U.S. applicationSer. No. 15/314,095, filed Nov. 28, 2016, which is a National Phaseentry of International Application No. PCT/JP2015/076814, filed Sep. 18,2015, which claims priority of International Application No.PCT/JP2014/081232, filed Nov. 26, 2014.

TECHNICAL FIELD

The present invention relates to a silicon carbide semiconductor deviceand a method of manufacturing the silicon carbide semiconductor device.

BACKGROUND ART

FIG. 18 is a cross-sectional view of a main part of a conventionalsilicon carbide semiconductor device 700.

As shown in FIG. 18, a conventional silicon carbide semiconductor device700 includes: an n⁺ type low resistance silicon carbide substrate 710;an n⁻ type epitaxial layer 712 formed on the n⁺ type low resistancesilicon carbide substrate 710; p type body regions 716 formed on asurface of the n⁻ type epitaxial layer 712; channel regions 718 formedon a surface of the p type body region 716; n⁺⁺ type source regions 720and p⁺⁺ type body contact regions 722; and gate electrodes 726 formed onat least the channel region 718 with a gate insulating film 724interposed therebetween. In FIG. 18, numeral 728 indicates an interlayerinsulation film, numeral 730 indicates a source electrode, and numeral732 indicates a drain electrode.

CITATION LIST Patent Literature

[PTL 1] Japanese patent No. 4502407

[PTL 2] Japanese patent No. 4173629

SUMMARY OF INVENTION Technical Problem

In a power MOSFET which uses silicon, a method has been popularly usedwhere a channel region is formed in a self-aligned manner by making useof a double diffusion method. Also in a power MOSFET which uses siliconcarbide, a method (first method) substantially equal to a doublediffusion method is disclosed (see the above-mentioned patent literature1, for example). However, in the first method, a diffusion coefficientof an impurity in silicon carbide is extremely small and hence,diffusion processing which is to be performed at a high temperature fora long time is necessary for forming a channel having a channel lengthsufficiently long for preventing the occurrence of a short channeleffect. Accordingly, the first method is not useful practically.

On the other hand, there has been also proposed a method (second method)where a channel region is formed in a self-aligned manner by making useof side walls (see the above-mentioned patent literature 2, forexample). However, in the second method, to form a channel region havinga channel length sufficiently long for preventing the occurrence of ashort channel effect, it is necessary to forma film (SiO₂ film, forexample) which constitutes a side wall with a large thickness.Accordingly, an upper surface of the side wall is remarkably rounded andhence, there arises a drawback that it is extremely difficult to formachannel region with an accurate channel length by such a method.

In view of the above, a method (third method) is considered where achannel region is formed by forming a p type body region and,thereafter, by forming an n⁺⁺ source region on the p type body region inan aligned manner. However, in this third method, the channel region isformed by performing a masking step twice and hence, there arises adrawback that it is difficult to accurately define a channel length dueto an error in mask alignment.

As a result, in this third method, it is necessary to set the channellength slightly longer by taking into account an error in maskalignment. Accordingly, a channel resistance and eventually an ONresistance of a semiconductor device are increased, and gate capacitanceis increased.

The present invention has been made to overcome the above-mentioneddrawback, and it is an object of the present invention to provide asilicon carbide semiconductor device and a method of manufacturing thesilicon carbide semiconductor device where a channel region can beformed by performing a masking step once, and a channel lengthsufficiently long for preventing the occurrence of a short channeleffect can be accurately defined in a practical process.

Solution to Problem

[1] A silicon carbide semiconductor device according to a first aspectof the present invention includes:

an epitaxial layer of a first conductive type;

a first semiconductor region of a first conductive type formed on asurface of the epitaxial layer of the first conductive type, and havinghigher impurity concentration than the epitaxial layer of the firstconductive type;

a body region of a second conductive type formed at a position deeperthan the first semiconductor region of the first conductive type;

a channel region of a second conductive type formed such that thechannel region of the second conductive type penetrates the firstsemiconductor region of the first conductive type from a surface side ofthe epitaxial layer of the first conductive type and reaches the bodyregion of the second conductive type, the channel region of the secondconductive type having lower impurity concentration than the body regionof the second conductive type;

a second semiconductor region of a first conductive type formed towardthe body region of the second conductive type from the front surfaceside of the epitaxial layer of the first conductive type, the secondsemiconductor region of the first conductive type having higher impurityconcentration than the first semiconductor region of the firstconductive type,

a body contact region of a second conductive type formed such that thebody contact region of the second conductive type penetrates the firstsemiconductor region of the first conductive type from the front surfaceside of the epitaxial layer of the first conductive type and reaches thebody region of the second conductive type, the body contact region ofthe second conductive type having higher impurity concentration than thebody region of the second conductive type; and

a gate electrode formed on at least the channel region of the secondconductive type with a gate insulating film interposed therebetween,wherein

the channel region of the second conductive type and the secondsemiconductor region of the first conductive type are formed at a planarposition where the first semiconductor region of the first conductivetype remains between the channel region of the second conductive typeand the second semiconductor region of the first conductive type, andout of boundary surfaces which are formed between the channel region ofthe second conductive type and the first semiconductor regions of thefirst conductive type, the boundary surface on an outer peripheral sideis positioned inside an outer peripheral surface of the body region ofthe second conductive type as viewed in a plan view.

In the silicon carbide semiconductor device according to the firstaspect of the present invention, the channel region of the secondconductive type may be also referred to as “the channel region of thesecond conductive type which is positioned in a region which penetratesthe first semiconductor region of the first conductive type from thefront surface side of the epitaxial layer of the first conductive typeand reaches the body region of the second conductive type, and has lowerimpurity concentration than the body region of the second conductivetype”. The body contact region of the second conductive type may be alsoreferred to as “the body contact region of the second conductive typewhich is positioned in a region which penetrates the first semiconductorregion of the first conductive type from the front surface side of theepitaxial layer of the first conductive type and reaches the body regionof the second conductive type, and has higher impurity concentrationthan the body region of the second conductive type”.

[2] In the silicon carbide semiconductor device according to the firstaspect of the present invention, it is preferable that an end portion ofthe gate electrode be positioned on the first semiconductor region ofthe first conductive type which remains between the channel region ofthe second conductive type and the second semiconductor region of thefirst conductive type as viewed in a plan view.[3] In the silicon carbide semiconductor device according to the firstaspect of the present invention, it is preferable that an end portion ofthe gate electrode be positioned on the second semiconductor region ofthe first conductive type as viewed in a plan view.[4] In the silicon carbide semiconductor device according to the firstaspect of the present invention, it is preferable that between the firstsemiconductor region of the first conductive type which remains betweenthe channel region of the second conductive type and the secondsemiconductor region of the first conductive type and the secondsemiconductor region of the first conductive type, a third semiconductorregion of a first conductive type having impurity concentration higherthan the first semiconductor region of the first conductive type andlower than the second semiconductor region of the first conductive typebe formed, and

an end portion of the gate electrode be positioned on the thirdsemiconductor region of the first conductive type as viewed in a planview.

[5] A silicon carbide semiconductor device according to a second aspectof the present invention includes:

an epitaxial layer of a first conductive type;

a body region of a second conducive type formed at a predetermined depthposition on a surface side of the epitaxial layer of the firstconductive type;

a channel region of a second conductive type formed such that thechannel region of the second conductive type reaches the body region ofthe second conductive type from the front surface side of the epitaxiallayer of the first conductive type, the channel region of the secondconductive type having lower impurity concentration than the body regionof the second conductive type;

a second semiconductor region of a first conductive type formed towardthe body region of the second conductive type from the front surfaceside of the epitaxial layer of the first conductive type, the secondsemiconductor region of the first conductive type having higher impurityconcentration than the epitaxial layer of the first conductive type,

a body contact region of a second conductive type formed such that thebody contact region of the second conductive type reaches the bodyregion of the second conductive type from the front surface side of theepitaxial layer of the first conductive type, the body contact region ofthe second conductive type having higher impurity concentration than thebody region of the second conductive type, and

a gate electrode formed on at least the channel region of the secondconductive type with a gate insulating film interposed therebetween,wherein

the channel region of the second conductive type and the secondsemiconductor region of the first conductive type are formed at a planarposition where the epitaxial layer of the first conductive type remainsbetween the channel region of the second conductive type and the secondsemiconductor region of the first conductive type, and out of boundarysurfaces which are formed between the channel region of the secondconductive type and the epitaxial layers of the first conductive type,the boundary surface on an outer peripheral side is positioned inside anouter peripheral surface of the body region of the second conductivetype as viewed in a plan view.

In the silicon carbide semiconductor device according to the secondaspect of the present invention, the channel region of the secondconductive type may be also referred to as “the channel region of thesecond conductive type which is positioned in a region which reaches thebody region of the second conductive type from the front surface side ofthe epitaxial layer of the first conductive type, and has lower impurityconcentration than the body region of the second conductive type”. Thebody contact region of the second conductive type may be also referredto as “the body contact region of the second conductive type which ispositioned in a region which reaches the body region of the secondconductive type from the front surface side of the epitaxial layer ofthe first conductive type, and has higher impurity concentration thanthe body region of the second conductive type”.

[6] In the silicon carbide semiconductor device according to the secondaspect of the present invention, it is preferable that an end portion ofthe gate electrode be positioned on the epitaxial layer of the firstconductive type which remains between the channel region of the secondconductive type and the second semiconductor region of the firstconductive type as viewed in a plan view.[7] In the silicon carbide semiconductor device according to the secondaspect of the present invention, it is preferable that an end portion ofthe gate electrode be positioned on the second semiconductor region ofthe first conductive type as viewed in a plan view.[8] In the silicon carbide semiconductor device according to the secondaspect of the present invention, it is preferable that between theepitaxial layer of the first conductive type which remains between thechannel region of the second conductive type and the secondsemiconductor region of the first conductive type and the secondsemiconductor region of the first conductive type, a third semiconductorregion of a first conductive type having impurity concentration higherthan the epitaxial layer of the first conductive type and lower than thesecond semiconductor region of the first conductive type be formed, and

an end portion of the gate electrode be positioned on the thirdsemiconductor region of the first conductive type as viewed in a planview.

[9]

A method of manufacturing the silicon carbide semiconductor deviceaccording to a third aspect of the present invention includes the stepsof:

preparing a silicon carbide semiconductor substrate provided with theepitaxial layer of the first conductive type;

forming the body region of the second conductive type on the frontsurface of the epitaxial layer of the first conductive type such that adepth position indicative of maximum concentration of an impurity of asecond conductive type is greater than a depth position which forms abottom surface of the channel region of the second conductive type;

forming the first semiconductor region of the first conductive type on asurface of the body region of the second conductive type;

forming the channel region of the second conductive type, the secondsemiconductor region of the first conductive type and a body contactregion of a second conductive type in the first semiconductor region ofthe first conductive type; and

forming the gate electrode on at least the channel region of the secondconductive type with a gate insulating film interposed therebetween,wherein

in the step of forming the channel region of the second conductive type,the second semiconductor region of the first conductive type and thebody contact region of the second conductive type, the channel region ofthe second conductive type, the second semiconductor region of the firstconductive type and the body contact region of the second conductivetype are formed at a planar position where the first semiconductorregion of the first conductive type remains between the channel regionof the second conductive type and the second semiconductor region of thefirst conductive type, and out of boundary surfaces which are formedbetween the channel region of the second conductive type and the firstsemiconductor regions of the first conductive type, the boundary surfaceon an outer peripheral side is positioned inside an outer peripheralsurface of the body region of the second conductive type as viewed in aplan view.

In the method of manufacturing the silicon carbide semiconductor deviceaccording to the third aspect of the present invention, it is preferablethat in the step of forming the gate electrode, the gate electrode beformed such that an end portion of the gate electrode is positioned onthe first semiconductor region of the first conductive type whichremains between the channel region of the second conductive type and thesecond semiconductor region of the first conductive type as viewed in aplan view.

In the method of manufacturing the silicon carbide semiconductor deviceaccording to the third aspect of the present invention, it is preferablethat in the step of forming the gate electrode, an end portion of thegate electrode be positioned on the second semiconductor region of thefirst conductive type as viewed in a plan view.

In the method of manufacturing the silicon carbide semiconductor deviceaccording to the third aspect of the present invention, it is preferablethat in the step of forming the channel region of the second conductivetype, the second semiconductor region of the first conductive type and abody contact region of a second conductive type, between the firstsemiconductor region of the first conductive type which remains betweenthe channel region of the second conductive type and the secondsemiconductor region of the first conductive type and the secondsemiconductor region of the first conductive type, a third semiconductorregion of a first conductive type having impurity concentration higherthan the first semiconductor region of the first conductive type andlower than the second semiconductor region of the first conductive typebe formed, and

in the step of forming the gate electrode, the gate electrode be formedsuch that an end portion of the gate electrode is positioned on thethird semiconductor region of the first conductive type as viewed in aplan view.

[10]

A method of manufacturing the silicon carbide semiconductor deviceaccording to a fourth aspect of the present invention includes the stepsof:

preparing a silicon carbide semiconductor substrate provided with theepitaxial layer of the first conductive type;

forming the body region of the second conductive type on a surface ofthe epitaxial layer of the first conductive type within a predetermineddepth region;

forming the channel region of the second conductive type, the secondsemiconductor region of the first conductive type and a body contactregion of a second conductive type on the front surface of the epitaxiallayer of the first conductive type; and

forming the gate electrode on at least the channel region of the secondconductive type with a gate insulating film interposed therebetween,wherein

in the step of forming the channel region of the second conductive type,the second semiconductor region of the first conductive type and thebody contact region of the second conductive type, the channel region ofthe second conductive type, the second semiconductor region of the firstconductive type and the body contact region of the second conductivetype are formed at a planar position where the epitaxial layer of thefirst conductive type remains between the channel region of the secondconductive type and the second semiconductor region of the firstconductive type, and out of boundary surfaces which are formed betweenthe channel region of the second conductive type and the epitaxiallayers of the first conductive type, the boundary surface on an outerperipheral side of the body region of the second conductive type ispositioned inside an outer peripheral surface of the body region of thesecond conductive type as viewed in a plan view.

In the method of manufacturing the silicon carbide semiconductor deviceaccording to the fourth aspect of the present invention, it ispreferable that in the step of forming the gate electrode, the gateelectrode be formed such that an end portion of the gate electrode ispositioned on the epitaxial layer of the first conductive type whichremains between the channel region of the second conductive type and thesecond semiconductor region of the first conductive type as viewed in aplan view.

In the method of manufacturing the silicon carbide semiconductor deviceaccording to the fourth aspect of the present invention, it ispreferable that in the step of forming the gate electrode, the gateelectrode be formed such that an end portion of the gate electrode ispositioned on the second semiconductor region of the first conductivetype as viewed in a plan view.

In the method of manufacturing the silicon carbide semiconductor deviceaccording to the fourth aspect of the present invention, it ispreferable that in the step of forming the channel region of the secondconductive type, the second semiconductor region of the first conductivetype and a body contact region of a second conductive type, between theepitaxial layer of the first conductive type which remains between thechannel region of the second conductive type and the secondsemiconductor region of the first conductive type and the secondsemiconductor region of the first conductive type, a third semiconductorregion of a first conductive type having impurity concentration higherthan the epitaxial layer of the first conductive type and lower than thesecond semiconductor region of the first conductive type be formed, and

in the step of forming the gate electrode, the gate electrode be formedsuch that an end portion of the gate electrode is positioned on thethird semiconductor region of the first conductive type as viewed in aplan view.

Advantageous Effects of Invention

According to the silicon carbide semiconductor device and the method ofmanufacturing the silicon carbide semiconductor device of the presentinvention, unlike the above-mentioned third method, the channel regioncan be formed by performing the masking step once and hence, it ispossible to eliminate a drawback that it is difficult to accuratelydefine a channel length due to an error in mask alignment. Further,according to the silicon carbide semiconductor device and the method ofmanufacturing the silicon carbide semiconductor device of the presentinvention, a predetermined channel length can be defined without makinguse of a double diffusion method and side walls adopted by theabove-mentioned first method and second method and hence, a channellength sufficiently long for preventing the occurrence of a shortchannel effect can be accurately defined in a practical process.

JP-A-2007-13058 discloses a silicon carbide semiconductor device(MOSFET800) provided with a channel region of a second conductive type(p type layer 827) which is formed such that the channel region of thesecond conductive type penetrates a first semiconductor region of afirst conductive type (n type stacked channel layer 824) and reaches abody region of a second conductive type (p type body layer 832) (seeFIG. 19). However, in the silicon carbide semiconductor device 800, abottom surface of the p type layer 827 is exposed to an n⁻ type driftlayer 834 and hence, with respect to a boundary surface between the ptype layer 827 and the n⁻ type drift layer 834, a depletion layerextends toward a surface of the p type layer 827 from the boundarysurface at a bottom surface portion of the p type layer 827 and hence, adrawback such as a change in a threshold value of a transistor or theoccurrence of a punch-through is liable to take place.

To the contrary, according to the silicon carbide semiconductor deviceof the present invention, the channel region of the second conductivetype and the second semiconductor region of the first conductive typeare formed at a planar position where out of boundary surfaces which areformed between the channel region of the second conductive type and thefirst semiconductor regions of the first conductive type, the boundarysurface on an outer peripheral side is positioned inside an outerperipheral surface of the body region of the second conductive type asviewed in a plan view and hence, the whole bottom surface of the channelregion of the second conductive type is covered by the body region ofthe second conductive type. Accordingly, there is no possibility thatthe depletion layer extends to the front surface of the channel regionof the second conductive type from the bottom surface of the channelregion of the second conductive type and hence, a drawback such as achange in a threshold value of a transistor or the occurrence of apunch-through minimally takes place.

JP-A-2014-29952 discloses a silicon carbide semiconductor device(MOSFET900) provided with a channel region of a second conductive typewhich is formed such that the channel region of the second conductivetype penetrates a first semiconductor region of a first conductive type(first region 911) and reaches a body region of a second conductive type(base region 920) (see FIG. 20). The channel region of the secondconductive type is a region 991 where the base region 920 and the firstregion 911 overlap with each other. In such a silicon carbidesemiconductor device 900, however, as can be also understood from FIG. 4and FIG. 5 of JP-A-2014-29952, the region 991 is formed by performing amasking step twice and hence, a drawback that it is difficult toaccurately define a channel length due to an error in mask alignmentcannot be overcome.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1A to FIG. 1C are views for describing a silicon carbidesemiconductor device 100 according to an embodiment 1. FIG. 1A is across-sectional view of a main part of the silicon carbide semiconductordevice 100, FIG. 1B is a cross-sectional view taken along a line A1-A1′in FIG. 1A, and FIG. 1C is a cross-sectional view taken along a lineA2-A2′ in FIG. 1A.

FIG. 2A and FIG. 2B are views for describing a step of manufacturing thesilicon carbide semiconductor device 100 according to the embodiment 1.FIG. 2A is a cross-sectional view of a main part showing a step ofmanufacturing the silicon carbide semiconductor device 100 according tothe embodiment 1, and FIG. 2B is a graph showing an impurityconcentration profile along a line A3-A3′ in FIG. 2A.

FIG. 3A and FIG. 3B are views for describing a step of manufacturing thesilicon carbide semiconductor device 100 according to the embodiment 1.FIG. 3A is a cross-sectional view of the main part showing a step ofmanufacturing the silicon carbide semiconductor device 100 according tothe embodiment 1, and FIG. 3B is a graph showing an impurityconcentration profile along a line A3-A3′ in FIG. 3A.

FIG. 4A and FIG. 4B are views for describing a step of manufacturing thesilicon carbide semiconductor device 100 according to the embodiment 1.FIG. 4A is a cross-sectional view of the main part showing a step ofmanufacturing the silicon carbide semiconductor device 100 according tothe embodiment 1, and FIG. 4B is a graph showing an impurityconcentration profile along a line A3-A3′ in FIG. 4A.

FIG. 5A and FIG. 5B are views for describing a step of manufacturing thesilicon carbide semiconductor device 100 according to the embodiment 1.FIG. 5A is a cross-sectional view of the main part showing a step ofmanufacturing the silicon carbide semiconductor device 100 according tothe embodiment 1, and FIG. 5B is a graph showing an impurityconcentration profile along a line A3-A3′ in FIG. 5A.

FIG. 6 is a cross-sectional view of the main part showing a step ofmanufacturing the silicon carbide semiconductor device 100 according tothe embodiment 1.

FIG. 7 is a cross-sectional view of the main part showing a step ofmanufacturing the silicon carbide semiconductor device 100 according tothe embodiment 1.

FIG. 8 is a cross-sectional view of the main part showing a step ofmanufacturing the silicon carbide semiconductor device 100 according tothe embodiment 1.

FIG. 9 is a cross-sectional view of the main part showing a step ofmanufacturing the silicon carbide semiconductor device 100 according tothe embodiment 1.

FIG. 10 is a cross-sectional view of a main part of a silicon carbidesemiconductor device 102 according to an embodiment 2.

FIG. 11 is a cross-sectional view of a main part of a silicon carbidesemiconductor device 104 of an embodiment 3.

FIG. 12 is a cross-sectional view of a main part of a silicon carbidesemiconductor device 106 according to an embodiment 4.

FIG. 13 is a cross-sectional view of the main part showing a step ofmanufacturing the silicon carbide semiconductor device 106 according tothe embodiment 4.

FIG. 14A to FIG. 14C are views for describing a silicon carbidesemiconductor device 108 according to an embodiment 5. FIG. 14A is across-sectional view of a main part of the silicon carbide semiconductordevice 108, FIG. 14B is a cross-sectional view taken along a line A1-A1′in FIG. 14A, and FIG. 14C is a cross-sectional view taken along a lineA2-A2′ in FIG. 14A.

FIG. 15A and FIG. 15B are views for describing a step of manufacturingthe silicon carbide semiconductor device 108 according to the embodiment5. FIG. 15A is a cross-sectional view of a main part showing a step ofmanufacturing the silicon carbide semiconductor device 108 according tothe embodiment 5, and FIG. 15B is a graph showing an impurityconcentration profile along a line A3-A3′ in FIG. 15A.

FIG. 16A and FIG. 16B are views for describing a step of manufacturingthe silicon carbide semiconductor device 108 according to the embodiment5. FIG. 16A is a cross-sectional view of a main part showing a step ofmanufacturing the silicon carbide semiconductor device 108 according tothe embodiment 5, and FIG. 16B is a graph showing an impurityconcentration profile along a line A3-A3′ in FIG. 16A.

FIG. 17 is a cross-sectional view of a main part of a silicon carbidesemiconductor device 200 according to an embodiment 6.

FIG. 18 is a cross-sectional view of a main part of a conventionalsilicon carbide semiconductor device 700.

FIG. 19 is a cross-sectional view of a main part of a silicon carbidesemiconductor device 800 described in JP-A-2007-13058. In FIG. 19,numeral 800 indicates a MOSFET, numerals 820 indicate source electrodes,numerals 822 indicate n⁺ type source layers, numerals 824 indicate ntype stack channel layers, numeral 826 indicates a gate oxide film,numerals 827 indicate p type layers, numeral 828 indicates a gateelectrode, numerals 832 indicate p type body layers, numeral 834indicates an n⁻ type drift layer, numeral 836 indicates an n⁺ type drainlayer, and numeral 838 indicates a drain electrode.

FIG. 20 is a cross-sectional view of a main part of a silicon carbidesemiconductor device 900 described in JP-A-2014-29952. In FIG. 20,numeral 900 indicates a transistor, numerals 901 indicate structuralbodies, a numeral 901 a indicates an upper surface, numeral 910indicates a drift region, numeral 911 indicates a first region, numeral912 indicates a second region, numeral 915 indicates a substrate,numeral 915 a indicates a first surface, numeral 915 b indicates asecond surface, numeral 920 indicates a base region, numeral 920 bindicates a lower end, numeral 930 indicates a source region, numeral940 indicates a gate insulating film, numeral 950 indicates a gateelectrode, numeral 951 indicates a source electrode, numeral 952indicates a drain electrode, numerals 955 indicate contacts, and numeral980 indicates an interlayer insulation film.

DESCRIPTION OF EMBODIMENTS

Hereinafter, a silicon carbide semiconductor device and a method ofmanufacturing the silicon carbide semiconductor device of the presentinvention are described in conjunction with embodiments shown in thedrawings.

Embodiment 1

1. Silicon Carbide Semiconductor Device According to Embodiment 1

A silicon carbide semiconductor device 100 according to an embodiment 1is a silicon carbide semiconductor device according to the first mode ofthe present invention. The silicon carbide semiconductor device 100according to the embodiment 1 is a power MOSFET.

In the embodiments described hereinafter, impurity concentration of aconductive type is set such that the impurity concentration is increasedin order of n⁻, n, n⁺, n⁺⁺ with respect to an n type, and in order ofp⁻, p, p⁺⁺ with respect to a p type. These symbols roughly indicate therelative magnitude of impurity concentration. For example, although ann⁺ type region has impurity concentration higher than an n⁻ type regionand an n type region and lower than an n⁺⁺ type region, it is not alwaysthe case where n⁺ type regions have the same impurity concentration.

As shown in FIG. 1, the silicon carbide semiconductor device 100according to the embodiment 1 includes: an n⁺ type low resistancesilicon carbide substrate 110; an n⁻ type epitaxial layer 112 formed ona surface of the n⁺ type low resistance silicon carbide substrate 110 ona first main surface side; n type semiconductor regions 114 formed on asurface of the n⁻ type epitaxial layer 112; p type body regions 116formed at positions deeper than the n type semiconductor regions 114; p⁻type channel regions 118 formed such that each p⁻ type channel region118 penetrates the n type semiconductor region 114 from the frontsurface side of the n⁻ type epitaxial layer 112, and reaches the p typebody region 116; n⁺⁺ type source regions 120 formed toward the p typebody region from the front surface side of the n⁻ type epitaxial layer112; p⁺⁺ type body contact regions 122 formed such that each p⁺⁺ typebody contact region 122 penetrates the n type semiconductor region 114from the front surface side of the n⁻ type epitaxial layer 112 andreaches the p type body region 116; and gate electrodes 126 each ofwhich is formed on at least the p⁻ type channel region 118 with a gateinsulating film 124 interposed therebetween. In the silicon carbidesemiconductor device 100 according to the embodiment 1, the p⁻ typechannel regions 118 and the n⁺⁺ type source regions 120 are formed at aplanar position where the n type semiconductor region 114 remainsbetween the p⁻ type channel region 118 and the n⁺⁺ type source region120, and out of boundary surfaces which are formed between the p⁻ typechannel region 118 and the n type semiconductor regions 114, theboundary surface on an outer peripheral side is positioned inside anouter peripheral surface of the p type body region 116 as viewed in aplan view.

In this embodiment, the n⁻ type epitaxial layer 112 corresponds to anepitaxial layer of a first conductive type of the present invention, then type semiconductor region 114 corresponds to a first semiconductorregion of a first conductive type of the present invention, the p typebody region 116 corresponds to a body region of a second conductive typeof the present invention, the p⁻ type channel region 118 corresponds toa channel region of a second conductive type of the present invention,the n⁺⁺ type source region corresponds to a second semiconductor regionof a first conductive type of the present invention, and the p⁺⁺ typebody contact region 122 corresponds to a body contact region of a secondconductive type.

In FIG. 1, the silicon carbide semiconductor device 100 is configuredsuch that all of the n type semiconductor regions 114, the p⁻ typechannel regions 118, the n⁺⁺ type source regions 120, and the p⁺⁺ typebody contact regions 122 have the same depth. However, it is not alwaysnecessary for these regions to have the same depth, and these regionsmay have different depths from each other.

In the silicon carbide semiconductor device 100 according to theembodiment 1, end portions of the gate electrode 126 are positioned onthe n type semiconductor regions 114 each of which remains between thep⁻ type channel region 118 and the n⁺⁺ type source region 120 as viewedin a plan view.

In the silicon carbide semiconductor device 100 according to theembodiment 1, as viewed in a plan view, a distance “a” between aboundary surface on an outer peripheral side out of boundary surfaceswhich are formed between the p⁻ type channel region 118 and the n typesemiconductor regions 114 and an outer peripheral surface of the p typebody region 116 satisfies the relationship of 0.1 μm≤a≤0.5 μm, forexample.

When the distance “a” is extremely small, due to a manufacturing error,there may be a case that a silicon carbide semiconductor device 100 ismanufactured where, as viewed in a plan view, a bottom surface of the p⁻type channel region 118 is brought into contact with the n typesemiconductor region 114 or the n⁻ type epitaxial layer 112. As aresult, there is a concern that a threshold value of the transistorchanges or punch-through occurs. On the other hand, when the distance“a” is excessively large, the number of channels which can be formed fora unit length in left and right directions in FIG. 1 is reduced andhence, an ON resistance is increased.

In FIG. 1, numeral 128 indicates interlayer insulation films, numeral130 indicates a source electrode, and numeral 132 indicates a drainelectrode. In this specification, with respect to the n⁺ type lowresistance silicon carbide substrate 110 and the n⁻ type epitaxial layer112, a main surface on a side where the n⁻ type epitaxial layer 112 isformed is referred to as a first main surface, and a main surface on aside opposite to the first main surface is referred to as a second mainsurface.

The n⁺ type low resistance silicon carbide substrate 110 is a lowresistance silicon carbide substrate formed using an n⁺ typesemiconductor doped with approximately 1 to 10×10¹⁶ cm⁻³ of nitrogen asan impurity, for example. As is well known, various kinds of siliconcarbides (SiC) exist such as 2H, 3C, 4H, 6H, 8H, 10H and 15R. Thesesilicon carbides have different crystal structures respectivelydepending on the arrangement of C atoms and Si atoms. However, siliconcarbide having any crystal structure can be used as a material forforming the n⁺ type low resistance silicon carbide substrate 110.

A thickness of the n⁻ type epitaxial layer 112 is approximately 5 to 15μm, for example. An impurity concentration of the n⁻ type epitaxiallayer 112 is approximately 0.5 to 1.5×10¹⁶ cm⁻³, for example.

A depth of the n type semiconductor region 114 is approximately 0.4 to0.8 μm, for example. An impurity concentration of the n typesemiconductor region 114 is approximately 2 to 3×10¹⁶ cm⁻³, for example.The n type semiconductor regions 114 are formed by implanting n typeimpurity ions (N ions, for example) from a surface of the n⁻ typeepitaxial layer 112 on a first main surface side.

A depth of a shallowest portion of the p type body region 116 isapproximately 0.05 to 0.5 μm, for example, and a depth of a deepestportion of the p type body region 116 is approximately 1.0 to 2.0 μm,for example. The depth position in the p type body region 116 where theimpurity concentration is highest is the depth position of 0.6 to 0.9μm, for example. The impurity concentration in a portion of the p typebody region 116 at such a position is approximately 2×10¹⁷ to 1×10¹⁹cm⁻³, for example. The p type body regions 116 are formed by implantingp type impurity ions (Al ions, for example) into the n⁻ type epitaxiallayer 112 from the front surface of the n⁻ type epitaxial layer 112 on afirst main surface side.

A depth of the p⁻ type channel region 118 is approximately 0.2 to 0.5 μm(excluding a depth of the p⁻ type channel region 118 which does notreach the p type body region 116), for example. An impurityconcentration of the p⁻ type channel region 118 is approximately 0.5 to5×10¹⁷ cm⁻³, for example. The p⁻ type channel regions 118 are formed byimplanting p type impurity ions (Al ions, for example) from the surfaceof the n⁻ type epitaxial layer 112 on a first main surface side.

A depth of the n⁺⁺ type source region 120 is approximately 0.2 to 0.6μm, for example. An impurity concentration of the n⁺⁺ type source region120 is approximately 1 to 50×10¹⁹ cm⁻³, for example. The n⁺⁺ type sourceregions 120 are formed by implanting n type impurity ions (P ions, forexample) from the surface of the n⁻ type epitaxial layer 112 on a firstmain surface side.

A depth of the p⁺⁺ type body contact region 122 is approximately 0.2 to0.6 μm (excluding a depth of the p⁺⁺ type body contact region 122 whichdoes not reach the p type body region 116), for example. An impurityconcentration of the p⁺⁺ type body contact region 122 is approximately 1to 50×10¹⁹ cm⁻³, for example. The p⁺⁺ type body contact regions 122 areformed by implanting p type impurity ions (Al ions, for example) fromthe surface of the n⁻ type epitaxial layer 112 on a first main surfaceside.

In the silicon carbide semiconductor device 100 according to theembodiment 1, a length along a lateral direction on a surface of a paperon which the silicon carbide semiconductor device 100 is drawn (channellength) of each p⁻ type channel region 118 is approximately 0.5 to 1.0μm, for example. Further, a distance between the p⁻ type channel region118 and the n⁺⁺ type source region 120 is approximately 0.1 to 0.3 μm,for example.

2. Method of Manufacturing a Silicon Carbide Semiconductor DeviceAccording to Embodiment 1

The silicon carbide semiconductor device 100 according to the embodiment1 can be manufactured by a manufacturing method (a method ofmanufacturing a silicon carbide semiconductor device according to theembodiment 1) described hereinafter.

Hereinafter, the method of manufacturing a silicon carbide semiconductordevice according to the embodiment 1 is described with reference to FIG.2 to FIG. 9 in the order of steps. In FIG. 2B, FIG. 3B, FIG. 4B and FIG.5B, a depth measured from a first main surface which forms a referencesurface is taken on an axis of abscissa. Symbol do indicates a depth ofthe first main surface, symbol d₁ indicates a depth of a bottom portionof the n type semiconductor region 114, symbol d₂ indicates a depth of abottom portion of the p type body region 116, symbol d₃ indicates adepth of a boundary surface between the n⁻ type epitaxial layer 112 anthe n⁺ type low resistance silicon carbide substrate 110, and symbol d₄indicates a depth of a second main surface.

1. Silicon Carbide Semiconductor Substrate Preparation Step

Firstly, a silicon carbide semiconductor substrate is prepared. Thesilicon carbide semiconductor substrate includes an n⁺ type lowresistance silicon carbide substrate 110, and an n⁻ type epitaxial layer112 formed on a surface of the n⁺ type low resistance silicon carbidesubstrate 110 on a first main surface side (see FIG. 2).

2. p Type Body Region Forming Step

Next, a predetermined mask M1 is formed on a surface of the n⁻ typeepitaxial layer 112 and, thereafter, Al ions are implanted into the n⁻type epitaxial layer 112 through the mask M1 thus forming p type bodyregions 116 (see FIG. 3A). At this stage of operation, the p type bodyregions 116 are formed on the surface of the n⁻ type epitaxial layer 112such that a depth position where a p type impurity exhibits the maximumconcentration becomes deeper than the depth position which is a bottomsurface of a p⁻ type channel region 118 (to be more specific, the depthposition of 0.6 to 0.9 μm, for example) (see FIG. 3B).

3. n Type Semiconductor Region Forming Step

Next, after the mask M1 is removed, n type impurity ions are implantedinto the surface of the n⁻ type epitaxial layer 112 thus forming an ntype semiconductor region 114 on the front surface of the n⁻ typeepitaxial layer 112 (see FIG. 4A). At this stage of operation, ionimplantation is performed under a condition where a concentration of ntype impurity is higher than a concentration of p type impurity in the ntype semiconductor region 114 (see FIG. 4B). The n type semiconductorregion 114 is formed over a whole region of an active region in thesilicon carbide semiconductor device 100.

4. Step for Forming p⁻ Type Channel Regions and the Like

Next, a p⁻ type channel region forming step where p⁻ type channelregions 118 are formed in the n type semiconductor region 114 (see FIG.5), a p⁺⁺ type body contact region forming step where p⁺⁺ type bodycontact regions 122 are formed in the n type semiconductor region 114(see FIG. 6), and an n⁺⁺ type semiconductor region forming step wheren⁺⁺ type source regions 120 are formed in the n type semiconductorregion 114 (see FIG. 7) are performed in this order.

(1) p⁻ Type Channel Region Forming Step

Firstly, a predetermined mask M2 is formed on the surface of the n⁻ typeepitaxial layer 112 and, thereafter, p type impurity ions (Al ions, forexample) are implanted into the n⁻ type epitaxial layer 112 through themask M2 thus forming the p⁻ type channel regions 118 in the n typesemiconductor region 114 (see FIG. 5A). At this stage of operation, thep⁻ type channel regions 118 are formed in the n type semiconductorregion 114 such that the p⁻ type channel regions 118 penetrate the ntype semiconductor region 114 and reach the p type body regions 116 (seeFIG. 5B). Further, p⁻ type channel regions 118 are formed at a planarposition where out of boundary surfaces which are formed between the p⁻type channel region 118 and the n type semiconductor regions 114, theboundary surface on an outer peripheral side is positioned inside anouter peripheral surface of the p type body region 116 as viewed in aplan view.

(2) p⁺⁺ Type Body Contact Region Forming Step

Next, after the mask M2 is removed, a predetermined mask M3 is formed ona surface of the n⁻ type epitaxial layer 112 and, thereafter, p typeimpurity ions (Al ions, for example) are implanted into the n⁻ typeepitaxial layer 112 through the mask M3 thus forming p⁺⁺ type bodycontact regions 122 in the n type semiconductor region 114 (see FIG. 6).At this stage of operation, the p⁺⁺ type body contact regions 122 areformed in the n type semiconductor region 114 such that the p⁺⁺ typebody contact regions 122 penetrate the n type semiconductor region 114and reach the p type body regions 116.

(3) n⁺⁺ Type Semiconductor Region Forming Step

Next, after the mask M3 is removed, a predetermined mask M4 is formed ona surface of the n⁻ type epitaxial layer 112 and, thereafter, n typeimpurity ions are implanted into the n⁻ type epitaxial layer 112 throughthe mask M4 thus forming n⁺⁺ type source regions 120 in the n typesemiconductor region 114 (see FIG. 7). At this stage of operation, then⁺⁺ type source regions 120 are formed in the n type semiconductorregion 114 such that the n⁺⁺ type source regions 120 penetrate the ntype semiconductor region 114 and reach the n type semiconductor region114. Further, the n⁺⁺ type source regions 120 are formed at a planarposition where the n type semiconductor region 114 remains between thep⁻ type channel region 118 and the n⁺⁺ type source region 120. The n⁺⁺type source regions 120 may be formed such that the n⁺⁺ type sourceregions 120 do not reach the p type body regions 116.

5. Gate Electrode Forming Step

Next, the mask M4 is removed and activation annealing is applied to thesubstrate and, thereafter, gate electrodes 126 are formed at least onthe p⁻ type channel regions 118 with a gate insulating film 124interposed therebetween (see FIG. 8).

6. Source Electrode and Drain Electrode Forming Step

Next, interlayer insulation films 128 are formed such that theinterlayer insulation film 128 covers the gate electrode 126 and, at thesame time, at least a portion of the n⁺⁺ type source region 120 and aportion of the p⁺⁺ type body contact region 122 are exposed (see FIG.9). Thereafter, a source electrode 130 is formed such that the sourceelectrode 130 covers the n⁻ type epitaxial layer 112 and the interlayerinsulation films 128 and, at the same time, is brought into ohmiccontact with the n⁺⁺ type source regions 120 and the p⁺⁺ type bodycontact regions 122. Further, a drain electrode 132 is formed on asurface (back surface) of the n⁺ type low resistance silicon carbidesubstrate 110 such that the drain electrode 132 is brought into ohmiccontact with the n⁺ type low resistance silicon carbide substrate 110(see FIG. 1).

By performing the above-mentioned steps, the silicon carbidesemiconductor device 100 according to the embodiment 1 can bemanufactured.

It is not always necessary to perform the p type body region formingstep, the n type semiconductor region forming step, and the step offorming the p⁻ type channel regions and the like in the above-mentionedorder. However, when there is a possibility that implanted ionsinterfere with each other, the design of the method of manufacturing thesilicon carbide semiconductor device 100 is facilitated by performingthe steps in the above-mentioned order. It is also not always necessaryto perform the p⁻ type channel region forming step, the p⁺⁺ type bodycontact region forming step and the n⁺⁺ type semiconductor regionforming step included in the step of forming the p⁻ type channel regionsand the like in the above-mentioned order.

3. Advantageous Effects Acquired by Silicon Carbide Semiconductor Deviceand Method of Manufacturing Silicon Carbide Semiconductor DeviceAccording to Embodiment 1

According to the silicon carbide semiconductor device 100 and the methodof manufacturing the silicon carbide semiconductor device 100 of theembodiment 1, unlike the third method described previously as one of theconventional methods, the channel regions can be formed by performingthe masking step once and hence, it is possible to overcome the drawbackof the conventional method that it is difficult to accurately define achannel length due to an error in mask alignment. Further, according tothe silicon carbide semiconductor device 100 and the method ofmanufacturing the silicon carbide semiconductor device 100 of theembodiment 1, a predetermined channel length can be defined withoutmaking use of a double diffusion method and side walls adopted by thefirst method and second method described previously as the conventionalmethods and hence, a channel length sufficiently long for preventing theoccurrence of a short channel effect can be accurately defined in apractical process.

Further, according to the silicon carbide semiconductor device 100 andthe method of manufacturing the silicon carbide semiconductor device 100of the embodiment 1, out of boundary surfaces which are formed betweenthe p⁻ type channel region 118 and the n type first semiconductorregions 114, the boundary surface on an outer peripheral side ispositioned inside an outer peripheral surface 116 a of the p type bodyregion 116 as viewed in a plan view and hence, the whole bottom surfaceof the p⁻ type channel region 118 is covered by the p type body region116. Accordingly, there is no possibility that the depletion layerextends to the surface of the p⁻ type channel region 118 of the p⁻ typechannel region 118 from the bottom surface of the p⁻ type channel region118 and hence, a drawback such as a change in a threshold value of atransistor or the occurrence of a punch-through minimally takes place.

Further, according to the silicon carbide semiconductor device 100 andthe method of manufacturing the silicon carbide semiconductor device 100of the embodiment 1, the p⁻ type channel regions 118 and the n⁺⁺ typesource regions 120 are formed at a planar position where the n typesemiconductor region 114 remains between the p⁻ type channel region 118and the n⁺⁺ type source region 120 and hence, in the p⁻ type channelregion forming step, portions of the n type semiconductor region 114into which p type impurity ions are implanted are formed into the p⁻type channel regions 118 with certainty so that channel regions can beformed by performing a masking step once.

Further, according to the silicon carbide semiconductor device 100 andthe method of manufacturing the silicon carbide semiconductor device 100of the embodiment 1, the end portions of the gate electrode 126 arepositioned on the n type semiconductor regions 114 each of which remainsbetween the p⁻ type channel region 118 and the n⁺⁺ type source region120 as viewed in a plan view. Accordingly, even if a slight positionaldisplacement occurs at the end portions of the gate electrode 126 at thetime of forming the gate electrodes 126, the gate electrode 126 coversthe channel regions with certainty. Accordingly, a channel length isalways maintained at a fixed value and hence, it is possible toaccurately define a desired channel length.

Further, according to the silicon carbide semiconductor device 100 andthe method of manufacturing the silicon carbide semiconductor device 100of the embodiment 1, n type impurities are introduced into a JFET regiondisposed directly below the gate electrode 126 so that a resistance inthe JFET region is lowered and hence, it is also possible to acquire anadvantageous effect that an ON resistance can be lowered.

In the silicon carbide semiconductor device 100 according to theembodiment 1, “the n⁺⁺ type source regions 120” and “the n typesemiconductor regions 114 each of which remains between the n⁺⁺ typesource region 120 and the p⁻ type channel region 118” form a sourceregion of the power MOSFET.

Embodiment 2

A silicon carbide semiconductor device 102 according to an embodiment 2is a silicon carbide semiconductor device according to the first mode ofthe present invention. The silicon carbide semiconductor device 102according to the embodiment 2 is a power MOSFET.

The silicon carbide semiconductor device 102 according to the embodiment2 basically has substantially the same configuration as the siliconcarbide semiconductor device 100 according to the embodiment 1. However,the silicon carbide semiconductor device 102 according to the embodiment2 differs from the silicon carbide semiconductor device 100 according tothe embodiment 1 with respect to a planar position of end portions ofeach gate electrode. That is, in the silicon carbide semiconductordevice 102 according to the embodiment 2, as shown in FIG. 10, endportions of each gate electrode 126 are positioned on n⁺⁺ type sourceregions 120 as viewed in a plan view.

In this manner, the silicon carbide semiconductor device 102 accordingto the embodiment 2 differs from the silicon carbide semiconductordevice 100 according to the embodiment 1 with respect to the planarposition of the end portions of the gate electrode. However, the siliconcarbide semiconductor device 102 according to the embodiment 2 includesp⁻ type channel regions 118 formed in the same manner as the siliconcarbide semiconductor device 100 according to the embodiment 1 andhence, a channel length sufficiently long for preventing the occurrenceof a short channel effect can be accurately defined in a practicalprocess. Further, a drawback such as a change in a threshold value of atransistor or the occurrence of a punch-through minimally takes place.

According to the silicon carbide semiconductor device 102 of theembodiment 2, the end portions of each gate electrode 126 are positionedon the n⁺⁺ type source regions 120 as viewed in a plan view.Accordingly, in the same manner as the silicon carbide semiconductordevice 100 according to the embodiment 1, even if a slight positionaldisplacement occurs at the end portions of the gate electrode 126 at thetime of forming the gate electrodes 126, the gate electrode covers thechannel regions with certainty. Accordingly, a channel length is alwaysmaintained at a fixed value and hence, it is possible to accuratelydefine a desired channel length.

According to the silicon carbide semiconductor device 102 of theembodiment 2, the end portions of each gate electrode 126 are positionedon the n⁺⁺ type source regions 120 as viewed in a plan view.Accordingly, compared to the case of the silicon carbide semiconductordevice 100 of the embodiment 1, a channel can be formed over the wholesurfaces of the p⁻ type channel regions 118 with certainty. Further, asurface of the n type semiconductor region 114 is brought into anaccumulation state and hence, a resistance is reduced. Accordingly, anON resistance is reduced compared to the silicon carbide semiconductordevice 100 of the embodiment 1.

In the case where the semiconductor device is a silicon carbidesemiconductor device, even when a surface of then type semiconductorregion 114 is brought into an accumulation state, the n⁺⁺ type sourceregion 120 has a lower resistance than the semiconductor region 114 ingeneral. Accordingly, it is desirable to arrange the n⁺⁺ type sourceregion 120 and the p⁻ type channel region 118 as close as possible whileleaving the n type semiconductor region 114 between the n⁺⁺ type sourceregion 120 and the p⁻ type channel region 118 with certainty even when amanufacturing error occurs. With such a configuration, an ON resistanceis further reduced.

The silicon carbide semiconductor device 102 according to the embodiment2 has substantially the same configuration as the silicon carbidesemiconductor device 100 according to the embodiment 1 except for theplanar position of the end portions of the gate electrode. Accordingly,the silicon carbide semiconductor device 102 of the embodiment 2 canacquire advantageous effects which are brought about by itsconfigurations which correspond to the configurations of the siliconcarbide semiconductor device 100 of the embodiment 1 out of theadvantageous effects which the silicon carbide semiconductor device 100according to the embodiment 1 can acquire.

Embodiment 3

A silicon carbide semiconductor device 104 of an embodiment 3 is asilicon carbide semiconductor device according to the first mode of thepresent invention. The silicon carbide semiconductor device 104according to the embodiment 3 is a power MOSFET.

The silicon carbide semiconductor device 104 according to the embodiment3 basically has substantially the same configuration as the siliconcarbide semiconductor device 100 according to the embodiment 1. However,the silicon carbide semiconductor device 104 according to the embodiment3 differs from the silicon carbide semiconductor device 100 according tothe embodiment 1 with respect to a planar position of end portions ofeach gate electrode. That is, in the silicon carbide semiconductordevice 104 according to the embodiment 3, as shown in FIG. 11, endportions of each gate electrode 126 are positioned on n⁺ typesemiconductor regions 134 each of which is formed between an n⁺⁺ typesource region 120 and an n type semiconductor region 114 as viewed in aplan view. In the embodiment 3, the n⁺ type semiconductor region 134corresponds to the third semiconductor region of a first conductive typeof the present invention.

A depth of the n⁺ type semiconductor region 134 is approximately 0.2 to0.6 μm, for example. An impurity concentration of the n⁺ typesemiconductor region 134 is approximately 0.5 to 10×10¹⁸ cm⁻³, forexample. The n⁺ type semiconductor regions 134 are formed by implantingn type impurity ions (N ions, for example) into n⁻ type epitaxial layer112 from a surface of the n⁻ type epitaxial layer 112 on a first mainsurface side.

In this manner, the silicon carbide semiconductor device 104 accordingto the embodiment 3 differs from the silicon carbide semiconductordevice 100 according to the embodiment 1 with respect to a planarposition of the end portions of the gate electrode. However, the siliconcarbide semiconductor device 104 according to the embodiment 3 includesp⁻ type channel regions 118 formed in the same manner as the siliconcarbide semiconductor device 100 according to the embodiment 1 andhence, a channel length sufficiently long for preventing the occurrenceof a short channel effect can be accurately defined in a practicalprocess. Further, a drawback such as a change in a threshold value of atransistor or the occurrence of a punch-through minimally takes place.

Further, according to the silicon carbide semiconductor device 104 ofthe embodiment 3, the end portions of the gate electrode 126 arepositioned on the n⁺ type semiconductor regions 134 each of which isformed between the n⁺⁺ type source region 120 and then typesemiconductor region 114. Accordingly, in the same manner as the siliconcarbide semiconductor device 100 of the embodiment 1, even if a slightpositional displacement occurs at the end portions of the gate electrode126 at the time of forming the gate electrodes 126, the gate electrodecovers the channel regions with certainty. Accordingly, a channel lengthis always maintained at a fixed value and hence, it is possible toaccurately define a desired channel length.

Further, according to the silicon carbide semiconductor device 104 ofthe embodiment 3, the end portions of each gate electrode 126 arepositioned on the n⁺ type semiconductor regions 134 each of which isformed between the n⁺⁺ type source region 120 and then typesemiconductor region 114. Accordingly, compared to the silicon carbidesemiconductor device 102 according to the embodiment 2, it is possibleto reduce surface roughness and crystal defects caused in siliconcarbide semiconductors which face the gate electrode 126 in an opposedmanner and into which ions are implanted and hence, a silicon carbidesemiconductor device which is minimally influenced by surface roughnessand crystal defects can be acquired. As the influence exerted by surfaceroughness and crystal defects, the lowering of a gate breakdown voltageor the lowering of reliability can be named, for example.

The silicon carbide semiconductor device 104 according to the embodiment3 has substantially the same configuration as the silicon carbidesemiconductor device 100 according to the embodiment 1 except for theplanar position of the end portions of the gate electrode. Accordingly,the silicon carbide semiconductor device 102 of the embodiment 3 canacquire advantageous effects which are brought about by itsconfigurations which correspond to the configurations of the siliconcarbide semiconductor device 100 of the embodiment 1 out of theadvantageous effects which the silicon carbide semiconductor device 100according to the embodiment 1 can acquire.

The silicon carbide semiconductor device 104 according to the embodiment3 differs from the silicon carbide semiconductor device 102 of theembodiment 2 with respect to a point that the end portions of the gateelectrode are formed on the n⁺ type semiconductor regions 134 in thesilicon carbide semiconductor device 104 according to the embodiment 3while the end portions of the gate electrode are formed on the n⁺⁺ typesource regions 120 in the silicon carbide semiconductor device 104according to the embodiment 2. However, in the same manner as theembodiment 2, a surface of then type semiconductor region 114 is broughtinto an accumulation state and hence, a resistance is reduced.Accordingly, an ON resistance is reduced compared to the silicon carbidesemiconductor device 100 of the embodiment 1.

In the case where the semiconductor device is a silicon carbidesemiconductor device, even when a surface of then type semiconductorregion 114 is brought into an accumulation state, the n⁺ typesemiconductor region 134 has a lower resistance than the semiconductorregion 114 in general. Accordingly, it is desirable to arrange the n⁺type semiconductor region 134 and the p⁻ type channel region 118 asclose as possible while leaving the n type semiconductor region 114between n⁺ type semiconductor region 134 and the p⁻ type channel region118 with certainty even when a manufacturing error occurs. With such aconfiguration, an ON resistance is further reduced.

In the silicon carbide semiconductor device 104 according to theembodiment 3, “the n⁺⁺ type source regions 120”, “the n⁺ typesemiconductor regions 134” and “the n type semiconductor regions 114each of which remains between the n⁺ type semiconductor region 134 andthe p⁻ type channel region 118” form the source region of the powerMOSFET.

Embodiment 4

A silicon carbide semiconductor device 106 according to an embodiment 4is a silicon carbide semiconductor device according to the first mode ofthe present invention. The silicon carbide semiconductor device 106according to the embodiment 4 is a power MOSFET. As shown in FIG. 12,the silicon carbide semiconductor device 106 according to the embodiment4 basically has substantially the same configuration as the siliconcarbide semiconductor device 100 according to the embodiment 1.

As described above, the silicon carbide semiconductor device 106according to the embodiment 4 has substantially the same configurationas the silicon carbide semiconductor device 100 according to theembodiment 1. However, as shown in FIG. 13, in a step of manufacturingthe silicon carbide semiconductor device according to the embodiment 4(n type semiconductor region forming step), n type impurity ions are notimplanted into portions which correspond to p⁺⁺ type body contactregions 122. Accordingly, the silicon carbide semiconductor deviceaccording to the embodiment 4 differs from the silicon carbidesemiconductor device 100 according to the embodiment 1 with respect to apoint that a silicon carbide semiconductor device to be manufactured isa silicon carbide semiconductor device where n type impurity ions arenot implanted into the portions which correspond to the p⁺⁺ type bodycontact regions 122.

In this manner, the silicon carbide semiconductor device 106 accordingto the embodiment 4 differs from the silicon carbide semiconductordevice 100 according to the embodiment 1 with respect to a point that ntype impurity ions are not implanted into the portions which correspondto the p⁺⁺ type body contact regions 122. However, the silicon carbidesemiconductor device according to the embodiment 4 includes p⁻ typechannel regions 118 formed in the same manner as the silicon carbidesemiconductor device 100 according to the embodiment 1 and hence, achannel length sufficiently long for preventing the occurrence of ashort channel effect can be accurately defined in a practical process.Further, a drawback such as a change in a threshold value of atransistor or the occurrence of a punch-through minimally takes place.

Further, according to the silicon carbide semiconductor device 106according to the embodiment 4, n type impurity ions are not implantedinto the portions which correspond to the p⁺⁺ type body contact regions122 and hence, it is also possible to acquire an advantageous effectthat contact resistance between a source electrode 130 and the p⁺⁺ typebody contact region can be further reduced.

The silicon carbide semiconductor device 106 according to the embodiment4 has substantially the same configuration as the silicon carbidesemiconductor device 100 according to the embodiment 1 except for that ntype impurity ions are not implanted into the portions which correspondto the p⁺⁺ type body contact regions 122. Accordingly, the siliconcarbide semiconductor device 106 of the embodiment 4 can acquireadvantageous effects which are brought about by its configurations whichcorrespond to the configurations of the silicon carbide semiconductordevice 100 of the embodiment 1 out of the advantageous effects which thesilicon carbide semiconductor device 100 according to the embodiment 1can acquire.

In the present invention, n type impurity ions may not be implanted intonot only the portions which correspond to the p⁺⁺ type body contactregions 122 but also portions of regions which correspond to the n⁺⁺type source region 120 disposed adjacently to the p⁺⁺ type body contactregions 122 at the time of forming the n type semiconductor regions 114.

Embodiment 5

A silicon carbide semiconductor device 108 according to an embodiment 5is a silicon carbide semiconductor device according to the second modeof the present invention. The silicon carbide semiconductor device 108according to the embodiment 5 is a power MOSFET. The silicon carbidesemiconductor device 108 according to the embodiment 5 basically hassubstantially the same configuration as the silicon carbidesemiconductor device 100 according to the embodiment 1.

As described above, the silicon carbide semiconductor device 108according to the embodiment 5 basically has substantially the sameconfiguration as the silicon carbide semiconductor device 100 accordingto the embodiment 1. However, as shown in FIG. 14A to FIG. 14C, thesilicon carbide semiconductor device 108 according to the embodiment 5differs from the silicon carbide semiconductor device 100 according tothe embodiment 1 with respect to a point that the silicon carbidesemiconductor device 108 according to the embodiment 5 does not includen type semiconductor regions. That is, in the silicon carbidesemiconductor device 108 according to the embodiment 5, “a region whichremains between an n⁺⁺ type source region 120 and a p⁻ type channelregion 118” is not “an n type semiconductor region” but is “an n⁻ typeepitaxial layer 112”.

As shown in FIG. 14A to FIG. 14C, the silicon carbide semiconductordevice 108 according to the embodiment 5 includes: an n⁺ type lowresistance silicon carbide substrate 110; an n⁻ type epitaxial layer 112formed on a surface of the n⁺ type low resistance silicon carbidesubstrate 110 on a first main surface side; p type body regions 116formed at predetermined depth positions on a surface side of the n⁻ typeepitaxial layer 112; p⁻ type channel regions 118 formed such that eachp⁻ type channel region 118 reaches the p type body region 116 from thefront surface side of the n⁻ type epitaxial layer 112; n⁺⁺ type sourceregions 120 each of which is formed toward the p type body region 116from the front surface side of the n⁻ type epitaxial layer 112; p⁺⁺ typebody contact regions 122 formed such that each p⁺⁺ type body contactregion 122 reaches the p type body region 116 from the front surfaceside of the n⁻ type epitaxial layer 112; and gate electrodes 126 each ofwhich is formed on at least the p⁻ type channel regions 118 with a gateinsulating film 124 interposed therebetween. The p⁻ type channel regions118 and the n⁺⁺ type source regions 120 are formed at a planar positionwhere the n⁻ type epitaxial layer 112 remains between the p⁻ typechannel region 118 and the n⁺⁺ type source region 120, and out ofboundary surfaces which are formed between the p⁻ type channel region118 and the n⁻ type epitaxial layers 112, the boundary surface on anouter peripheral side is positioned inside an outer peripheral surfaceof the p type body region 116 as viewed in a plan view.

The silicon carbide semiconductor device 108 according to the embodiment5 can be manufactured by performing substantially the same steps as themethod of manufacturing a silicon carbide semiconductor device accordingto the embodiment 1 except for that, in a p type body region formingstep, the p type body regions 116 are formed at predetermined depthregions on a surface of the n⁻ type epitaxial layer 112 (see FIG. 15),and the p⁻ type channel regions 118 (see FIG. 16), the n⁺⁺ type sourceregions 120 and the p⁺⁺ type body contact regions 122 are formed on thesurface of the n⁻ type epitaxial layer 112.

In this manner, the silicon carbide semiconductor device 108 accordingto the embodiment 5 differs from the silicon carbide semiconductordevice 100 according to the embodiment 1 with respect to a point thatthe silicon carbide semiconductor device 108 according to the embodiment5 does not include n type semiconductor regions. However, the siliconcarbide semiconductor device 108 according to the embodiment 5 includesthe p⁻ type channel regions 118 formed in the same manner as the siliconcarbide semiconductor device 100 according to the embodiment 1 andhence, a channel length sufficiently long for preventing the occurrenceof a short channel effect can be accurately defined in a practicalprocess. Further, a drawback such as a change in a threshold value of atransistor or the occurrence of a punch-through minimally takes place.

Further, according to the silicon carbide semiconductor device of theembodiment 5, it is also possible to acquire an advantageous effect thatan n type semiconductor region forming step can be omitted.

The silicon carbide semiconductor device according to the embodiment 5has substantially the same configuration as the silicon carbidesemiconductor device 100 according to the embodiment 1 except for thatthe silicon carbide semiconductor device according to the embodiment 5does not include the n type semiconductor regions. Accordingly, thesilicon carbide semiconductor device 108 of the embodiment 5 can acquireadvantageous effects which are brought about by its configurations whichcorrespond to the configurations of the silicon carbide semiconductordevice 100 of the embodiment 1 out of the advantageous effects which thesilicon carbide semiconductor device 100 according to the embodiment 1can acquire.

Embodiment 6

A silicon carbide semiconductor device 200 according to the embodiment 6is a silicon carbide semiconductor device according to the first mode ofthe present invention. The silicon carbide semiconductor device 200according to the embodiment 6 is an IGBT. FIG. 17 is a cross-sectionalview of a main part of the silicon carbide semiconductor device 200according to the embodiment 6. In FIG. 17, numeral 210 indicates a p⁺type low resistance silicon carbide substrate, numeral 212 indicates ann⁻ type epitaxial layer, numeral 214 indicates n type semiconductorregions, numerals 216 indicates p type body regions, numeral 218indicates p⁻ type channel regions, numeral 220 indicates n⁺⁺ typeemitter regions, numeral 222 indicates p⁺⁺ type body contact regions,numeral 224 indicates a gate insulation layer, numeral 226 indicates agate electrode, numeral 228 indicates interlayer insulation layers,numeral 230 indicates an emitter electrode, and numeral 232 indicates acollector electrode. In the embodiment 6, the n⁺⁺ type emitter regions220 correspond to second semiconductor regions of a first conductivetype of the present invention.

The silicon carbide semiconductor device 200 according to the embodiment6 basically has substantially the same configuration as the siliconcarbide semiconductor device 100 according to the embodiment 1. However,as shown in FIG. 17, the silicon carbide semiconductor device 200according to the embodiment 6 differs from the silicon carbidesemiconductor device 100 according to the embodiment 1 with respect to apoint that the silicon carbide semiconductor device 200 according to theembodiment 6 includes the p⁺ type low resistance silicon carbidesubstrate 210 as a low resistance silicon carbide substrate. That is,the silicon carbide semiconductor device 200 according to the embodiment6 is an IGBT.

In this manner, the silicon carbide semiconductor device according tothe embodiment 6 differs from the silicon carbide semiconductor device100 according to the embodiment 1 with respect to a point that thesilicon carbide semiconductor device according to the embodiment 6includes the p⁺ type low resistance silicon carbide substrate 210 as thelow resistance silicon carbide substrate, and the silicon carbidesemiconductor device according to the embodiment 6 is an IGBT. However,the silicon carbide semiconductor device according to the embodiment 6includes the p⁻ type channel regions 118 formed in the same manner asthe silicon carbide semiconductor device 100 according to the embodiment1 and hence, a channel length sufficiently long for preventing theoccurrence of a short channel effect can be accurately defined in apractical process. Further, a drawback such as a change in a thresholdvalue of a transistor or the occurrence of a punch-through minimallytakes place.

The silicon carbide semiconductor device 200 according to the embodiment6 has substantially the same configuration as the silicon carbidesemiconductor device 100 according to the embodiment 1 except for thatthe silicon carbide semiconductor device 200 according to the embodiment6 includes the p⁺ type low resistance silicon carbide substrate 210 asthe low resistance silicon carbide substrate and the silicon carbidesemiconductor device 200 according to the embodiment 6 is an IGBT.Accordingly, the silicon carbide semiconductor device 200 of theembodiment 6 can acquire advantageous effects which are brought about byits configurations which correspond to the configurations of the siliconcarbide semiconductor device 100 of the embodiment 1 out of theadvantageous effects which the silicon carbide semiconductor device 100according to the embodiment 1 can acquire.

The present invention has been described heretofore with reference tothe above-mentioned embodiments. However, the present invention is notlimited to the above-mentioned embodiments. Various modifications areconceivable without departing from the gist of the present invention.

(1) In the above-mentioned respective embodiments, the present inventionhas been described assuming a first conductive type as an n type, and asecond conductive type as a p type. However, the present invention isnot limited to the above. The first conductive type may be a p type andthe second conductive type may be an n type.(2) In the above-mentioned respective embodiments, the present inventionhas been described by taking the silicon carbide semiconductor devicewhere the transistor is formed into a stripe shape as an example.However, the present invention is not limited to the above. The presentinvention is also applicable to a silicon carbide semiconductor devicewhere a transistor is formed into a square shape.

REFERENCE SIGNS LIST

-   100, 102, 104, 108, 200, 700: silicon carbide semiconductor-   device-   110, 710: n⁺ type low resistance silicon carbide substrate-   112, 212, 712: n⁻ type epitaxial layer-   114, 214, 714: n type semiconductor region-   116, 216, 716: p type body region-   116 a: outer peripheral surface of p type body region 116-   118, 218, 318: p⁻ type channel region-   120, 720: n⁺⁺ type source region-   122, 222, 722: p⁺⁺ type body contact region-   124, 224, 724: gate insulation layer-   126, 226, 726: gate electrode-   128, 228, 728: interlayer insulation layer-   130, 730: source electrode-   132, 720: drain electrode-   134: n⁺ type semiconductor region-   210: p⁺ type low resistance silicon carbide substrate-   220: n⁺⁺ type emitter region-   230: emitter electrode-   232: collector electrode-   M1, M2, M3, M4, M5, M6: mask

The invention claimed is:
 1. A method of manufacturing a silicon carbidesemiconductor device comprising: an epitaxial layer of a firstconductive type; a first semiconductor region of a first conductive typeformed on a surface of the epitaxial layer of the first conductive type,and having higher impurity concentration than that of the epitaxiallayer of the first conductive type; a body region of a second conductivetype formed at a position deeper than that of the first semiconductorregion of the first conductive type; a channel region of a secondconductive type formed such that the channel region of the secondconductive type penetrates the first semiconductor region of the firstconductive type from a surface of the epitaxial layer of the firstconductive type, reaches the body region of the second conductive type,and defines a first part of the first semiconductor region of the firstconductive type formed entirely on the body region of the secondconductive type and a second part of the first semiconductor region ofthe first conductive type formed partially on the body region of thesecond conductive type, wherein the first part of the firstsemiconductor region of the first conductive type and the channel regionof the second conductive type define a first boundary surface, and thesecond part of the first semiconductor region of the first conductivetype and the channel region of the second conductive type define asecond boundary surface, the channel region of the second conductivetype having lower impurity concentration than that of the body region ofthe second conductive type; a second semiconductor region of a firstconductive type formed toward the body region of the second conductivetype from the surface of the epitaxial layer of the first conductivetype, the second semiconductor region of the first conductive typehaving higher impurity concentration than that of the firstsemiconductor region of the first conductive type; a body contact regionof a second conductive type formed such that the body contact region ofthe second conductive type penetrates the first semiconductor region ofthe first conductive type from the surface of the epitaxial layer of thefirst conductive type and reaches the body region of the secondconductive type, the body contact region of the second conductive typehaving higher impurity concentration than that of the body region of thesecond conductive type; and a gate electrode formed on at least thechannel region of the second conductive type with a gate insulating filminterposed therebetween, wherein the channel region of the secondconductive type and the second semiconductor region of the firstconductive type are formed at a planar position where the first part ofthe first semiconductor region of the first conductive type remainsbetween the channel region of the second conductive type and the secondsemiconductor region of the first conductive type, and separates thechannel region of the second conductive type from the secondsemiconductor region of the first conductive type, and the secondboundary surface is positioned on the body region of the secondconductive type as viewed in a plan view, wherein the method comprisingthe steps of: preparing a silicon carbide semiconductor substrateprovided with the epitaxial layer of the first conductive type; formingthe body region of the second conductive type on the surface of theepitaxial layer of the first conductive type such that a depth where amaximum concentration of an impurity of a second conductive type isdeeper than a depth position of a bottom surface of the channel region;forming the first semiconductor region of the first conductive type on asurface of the body region of the second conductive type; forming thechannel region of the second conductive type, the second semiconductorregion of the first conductive type and a body contact region of asecond conductive type in the first semiconductor region of the firstconductive type, the body contact region of the second conductive typepenetrating the first semiconductor region of the first conductive typefrom the surface of the epitaxial layer of the first conductive type andreaches the body region of the second conductive type; and forming thegate electrode on at least the channel region of the second conductivetype with a gate insulating film interposed therebetween, wherein in thestep of forming the channel region of the second conductive type, thesecond semiconductor region of the first conductive type and the bodycontact region of the second conductive type, the channel region of thesecond conductive type, the second semiconductor region of the firstconductive type and the body contact region of the second conductivetype are formed at a planar position where the first part of the firstsemiconductor region of the first conductive type remains between thechannel region of the second conductive type and the secondsemiconductor region of the first conductive type, and the secondboundary surface is positioned on the body region of the secondconductive type as viewed in a plan view.
 2. The method according toclaim 1, wherein the forming the gate electrode comprises forming an endportion of the gate electrode on the first semiconductor region of thefirst conductive type which remains between the channel region of thesecond conductive type and the semiconductor region of the firstconductive type as viewed in a plan view.
 3. The method according toclaim 1, wherein the forming the gate electrode comprises forming an endportion of the gate electrode on the semiconductor region of the firstconductive type as viewed in a plan view.
 4. The method according toclaim 1, further comprising a step of forming a third semiconductorregion of a first conductive type between (1) the first part of thefirst semiconductor region of the first conductive type, which remainsbetween (a) the channel region of the second conductive type and (b) thesecond semiconductor region of the first conductive type and (2) thesecond semiconductor region of the first conductive type, wherein thethird semiconductor region of a first conductive type has impurityconcentration that is higher than that of the first semiconductor regionof the first conductive type and lower than that of the secondsemiconductor region of the first conductive type, and the forming thegate electrode comprises forming an end portion of the gate electrode onthe third semiconductor region of the first conductive type as viewed ina plan view.
 5. A method of manufacturing a silicon carbidesemiconductor device comprising: an epitaxial layer of a firstconductive type; a body region of a second conducive type formed at apredetermined depth position on a surface of the epitaxial layer of thefirst conductive type; a channel region of a second conductive typeformed such that the channel region of the second conductive typereaches the body region of the second conductive type from the surfaceof the epitaxial layer of the first conductive type, the channel regionof the second conductive type having lower impurity concentration thanthat of the body region of the second conductive type; a semiconductorregion of a first conductive type formed toward the body region of thesecond conductive type from the surface of the epitaxial layer of thefirst conductive type, the semiconductor region of the first conductivetype having higher impurity concentration than that of the epitaxiallayer of the first conductive type; a body contact region of a secondconductive type formed such that the body contact region of the secondconductive type reaches the body region of the second conductive typefrom the surface of the epitaxial layer of the first conductive type,the body contact region of the second conductive type having higherimpurity concentration than that of the body region of the secondconductive type, and a gate electrode formed on at least the channelregion of the second conductive type with a gate insulating filminterposed therebetween, wherein the channel region of the secondconductive type and the semiconductor region of the first conductivetype are formed at a planar position where the epitaxial layer of thefirst conductive type remains between the channel region of the secondconductive type and the semiconductor region of the first conductivetype and separates the channel region of the second conductive type fromthe semiconductor region of the first conductive type, and a boundarydefined between the channel region of the second conductive type and theepitaxial layer of the first conductive type is positioned on the bodyregion of the second conductive type as viewed in a plan view, whereinthe method comprising the steps of: preparing a silicon carbidesemiconductor substrate provided with the epitaxial layer of the firstconductive type; forming the body region of the second conductive typeon a surface of the epitaxial layer of the first conductive type withina predetermined depth region; forming the channel region of the secondconductive type, the second semiconductor region of the first conductivetype and a body contact region of a second conductive type on thesurface of the epitaxial layer of the first conductive type; and formingthe gate electrode on at least the channel region of the secondconductive type with a gate insulating film interposed therebetween,wherein in the step of forming the channel region of the secondconductive type, the semiconductor region of the first conductive typeand the body contact region of the second conductive type, the channelregion of the second conductive type, the semiconductor region of thefirst conductive type and the body contact region of the secondconductive type are formed at a planar position where the epitaxiallayer of the first conductive type remains between the channel region ofthe second conductive type and the semiconductor region of the firstconductive type, and the boundary defined between the channel region ofthe second conductive type and the epitaxial layer of the firstconductive type is positioned on the body region of the secondconductive type as viewed in a plan view.
 6. The method according toclaim 5, wherein the forming the gate electrode comprises forming an endportion of the gate electrode on the epitaxial layer of the firstconductive type which remains between the channel region of the secondconductive type and the semiconductor region of the first conductivetype as viewed in a plan view.
 7. The method according to claim 5,wherein the forming the gate electrode comprises forming an end portionof the gate electrode on the semiconductor region of the firstconductive type as viewed in a plan view.
 8. The method according toclaim 5, further comprising a step of forming a third semiconductorregion of a first conductive type between (1) a portion of the epitaxiallayer of the first conductive type and the semiconductor region of thefirst conductive type, wherein the portion of the epitaxial layer of thefirst conductive type remains between (a) the channel region of thesecond conductive type and (b) the semiconductor region of the firstconductive type, and (2) the semiconductor region of the firstconductive type, wherein the third semiconductor region of a firstconductive type has impurity concentration that is higher than that ofthe epitaxial layer of the first conductive type and lower than that ofthe semiconductor region of the first conductive type, and the formingthe gate electrode comprises forming an end portion of the gateelectrode on the third semiconductor region of the first conductive typeas viewed in a plan view.